In many modern cordless communications systems, use is made of time division multiple access techniques, TDMA, in which both the base station and the cordless terminal have to send and receive bursts of information in a perfectly defined time slot so that they are able to communicate with each other without loss of bursts and without interfering with other channels located in different time slots.
For this reason both parts must have a common timebase that makes this possible.
The manner in which this common timebase is normally achieved is that the base station generates a timebase, termed master timebase, while the cordless terminal has a timebase, termed slave timebase, that has to lock on to that of the base station. This locking is necessary because drifting between the two timebases occurs as a result of using different oscillators to generate them.
To produce the necessary synchronisation between the timebases of the base station and of the cordless terminal, the latter has to "listen" continuously the base station and to continuously compensate for any small shifts that occur in its own timebase, so that when it has to receive or send a burst, the timebases of both parts are already synchronised and communication can take place between the two parts without problems resulting from a lack of burst synchronisation.
The fact that there are some periods of time during which the cordless terminal is not receiving bursts generated in the base station is not important if these are not long enough such that the drift between the two timebases when bursts from the base station are received once again, makes correct resynchronisation impossible.
It is therefore necessary for the cordless terminal to be permanently "listening" the base station, resulting in an unnecessary current consumption that has a major impact on the duration of the terminal batteries. This is particularly important for the so-called pocket terminals, the batteries of which must have considerable autonomy.
This problem becomes especially significant when the terminal is used infrequently, and it can occur that the batteries become discharged after a certain number of hours even without the user having actively employed the terminal.